Electrochemical cell for facilitating hermeticity leakage testing of an electrical feedthrough

Abstract

An electrical feedthrough, including a metal ferrule, an electrical lead, a glass seal for centrally locating the electrical lead axially within ferrule, for electrically isolating the electrical lead from the ferrule and for hermetically sealing the feedthrough assembly, which further includes an injection molded insulating material extending between the ferrule and lead and a fluorocarbon washer positioned adjacent the inner surface of the glass seal. The fluorocarbon washer is capable of retaining helium and allows for the hermeticity leakage testing of the glass seal. Such a feedthrough is particularly useful in hermetically sealed electrochemical cells wherein the insulated portion of the feedthrough is placed in the cell and the uninsulated portion of the ferrule is welded to or forms the cell cover, and the electrical lead is electrically connected to cell components, such as the anode, within the cell. The hermeticity testing of the aforementioned cell is accomplished by constructing the electrical feedthrough with the teflon washer in position; attaching the feedthrough to the hermetically sealed cells; placing the completed electrochemical cell in a pressurized atmosphere of a test gas, such as helium, for a period of time to force the test gas through the glass seal into the chamber containing the fluorocarbon washer, whereby the fluorocarbon washer absorbs helium gas; and examining the electrochemical cell for leakage of any of the helium back out through the glass seal. Gross and fine leakage testing may be accomplished by respectively observing the escape of the test gas at atmospheric pressure and drawing a vacuum on the electrical feedthrough and testing for the escape of the test gas with a mass spectrometer.

Having described the invention by way of illustration, the exclusive property right therein is claimed as follows: 
     
       1. An electrical feedthrough for a hermetically sealed container comprising: a conductive lead having interior and exterior extending portions;   a ferrule carried by the container and having a fixed barrel length and an annular portion surrounding a portion of the lead length;   glass seal means for hermetically supporting the lead in the ferrule and insulating the lead therefrom, said seal means having interior and exterior surfaces and filling only a portion of the barrel length of said ferrule leaving an unfilled space within the remaining portion of said ferrule adjacent said interior surface;   gas retaining material body means fitted within said unfilled portion of said ferrule adjacent to the interior surface of said seal means; and   plastic body means molded to the annular portion of said ferrule and to at least a portion of the interior extending portion of said conductive lead for retaining said gas retaining body means positioned within said ferrule adjacent said interior surface and for protecting the interior portion of the feedthrough from contact with the contents of the sealed container.   
     
     
       2. The electrical feedthrough of claim 1 wherein said gas retaining material body means comprises an element of polytetrafluoroethylene. 
     
     
       3. The electrical feedthrough of claim 1 wherein said body is in the form of a washer surrounding said conductive lead. 
     
     
       4. An electrochemical cell having anode and cathode electrode means enclosed in a container and feedthrough extending through a wall of the container for electrically connecting one of the electrode means, the feedthrough comprising: a conductive lead having a first portion extending into the container and connected to one of the electrode means and a second portion extending away from the container;   a ferrule carried by the container and having a fixed barrel length a portion extending into the container, the ferrule surrounding a further portion of the conductive lead length;   glass seal means for hermetically supporting the lead in the ferrule and insulating the lead therefrom, said seal means having interior and exterior surfaces and filling only a portion of the barrel length of said ferrule leaving an unfilled space within the remaining portion of said ferrule adjacent said interior surface;   gas retaining material body means fitted within said unfilled portion of said ferrule adjacent to the interior surface of said seal means; and   plastic body means molded to the annular portion of said barrel and to at least a portion of the interior extending portion of said conductive lead for retaining said gas retaining body means positioned within said ferrule adjacent said interior surface and for protecting the interior portion of the feedthrough from contact with the cell contents.   
     
     
       5. The electrochemical cell of claim 4 wherein said gas retaining material body means comprises an element of polytetrafluoroethylene. 
     
     
       6. The electrochemical cell of claim 5 wherein said body is in the form of a washer surrounding said conductive lead.